This kind of camera suffers from an effect due to how the sensor is read. If it reads data row by row you get a wobbling effect. If it reads a whole frame at once you get a more stable picture. This kind of operation is typical of much more expensive cameras.I tried it on the windscreen and it was the same, it's ok unless the road is very rough. My front camera is ok, but a totally different type of mount.
Tony.
It might be a combination of the mount flexibility and the way the camera works. You may never be able to eradicate it sadly.


